A radar summary chart, Figure 7-1, graphically
displays a collection of radar weather reports (SDs). Figures
1-1 and 1-2 depict the National Weather Service
radar network. This computer-generated chart is constructed from regularly
scheduled radar observations and is valid at the time of the reports (H+35),
i.e., 35 minutes past each hour. These charts are available between 16
and 24 hours daily depending on the system being used. The chart displays
the type of precipitation echoes, their intensity, intensity trend, configuration,
coverage, echo tops and bases, and movement. Severe weather watches are
plotted if they are in effect when the chart is valid.

ECHO TYPE

Radar primarily detects particles of precipitation size within a cloud
or falling from a cloud. The type of precipitation can be determined by
the radar operator from the scope presentation in combination with other
sources. Table 7-2 lists the symbols used to denote
types of precipitation.

INTENSITY AND INTENSITY TREND

The intensity is obtained from the Video Integrator Processor (VIP)
and is indicated on the chart by contours. The six VIP levels are combined
into three contours as indicated in Table 7-2. In
Figure 7-1 over southwest Nebraska and northwest
Kansas, there is an area of precipitation depicted by one contour. The
area would have an intensity of VIP level 1 and possibly VIP level 2. Whether
there is a VIP level 2 in the area cannot be determined. However, what
can be said is that the maximum intensity is definitely below VIP level
3. When determining intensity levels from this chart, it is recommended
that the maximum possible intensity be used. To determine the actual maximum
VIP level, the radar weather report (SD) for that time period should be
examined.

The intensity trend is indicated by a symbol plotted beside the precipitation
type. Looking at Figure 7-1, the rain showers in
Virginia (RW-) have decreased in intensity since the last observation.
The absence of a trend symbol indicates no change. The area of light to
moderate rain (R) and rain showers (RW) over Tennessee and Kentucky, have
not changed in intensity from the previous observation. The rain showers
in southern California (RW+) have increased in intensity since the last
observation.

The actual intensity for frozen precipitation cannot be determined from
the contours as the intensity levels are only correlated to liquid precipitation.
Intensity trend for frozen precipitation is neither reported on a SD nor
the radar summary chart. The "SW+" for the precipitation area in Colorado
means the area of snow showers is new, i.e. it was not reported on the
last observation. A "S" on the chart means an area of snow is indicated
by radar with no reference to intensity trend. Remember the intensity trend
symbols; (-) decreasing, (no symbol) no change, and (+) increasing refer
to liquid precipitation only.

It is important to remember that intensity on the radar summary chart
is shown by contours and not by the symbol following the type of precipitation.

ECHO CONFIGURATION AND COVERAGE

The configuration is the arrangement of echoes. There are three designated
arrangements; a LINE of echoes, an AREA of echoes, and an isolated CELL.
See Section 3 under radar reports for definitions of the three configurations.

Coverage is simply the area covered by echoes. All of the hatched area
inside of the contours on the chart is considered to be covered by echoes.
When the echoes are reported as a LINE, a line will be drawn through them
on the chart. Where there is 8/10 coverage or more, the line is labeled
as solid (SLD) at both ends. In the absence of this label it can be assumed
that there is less than 8/10 coverage. For example in Figure 7-1, there
is a solid line of thunderstorms with intense to extreme rain showers along
the coast of the Florida panhandle.

ECHO HEIGHTS

Echo heights in locations with radars designed for weather detection
are obtained by use of range height indicators and are PRECIPITATION tops
and bases. In those areas not served by National Weather Service radars,
the tops are obtained from pilot reports and are actual CLOUD tops. Usually,
echo height will be missing in the western mountain regions because ARTCC
radars are used.

Heights are displayed in hundreds of feet MSL and should be considered
only as approximations because of radar limitations. Tops are entered above
a short line while any available bases are entered below. The top height
displayed is the highest in the indicated area.

For example:

220 Bases 8,000 feet, Maximum top 22,000 feet
080

500 Bases at surface, Maximum top 50,000 feet

020 Bases 2,000 feet, Maximum top either missing or reported
in another place

Absence of a figure below the line indicates that the echo base is at
or near the surface. Radar detects tops more readily than bases because
precipitation usually reaches the ground. For example, over Kentucky and
Tennessee, (see Figure 7-1), the maximum precipitation
top in the area is 15,000 to 17,000 feet MSL. The location is indicated
by a line drawn from the top value to the location of that top. Further
west, the area of snow over Nebraska and Kansas has a base of 7,000 feet
MSL and a top of 18,000 feet MSL.

ECHO MOVEMENT

Individual cell movement is indicated by an arrow with the speed in
knots entered as a number at the top of the arrow head. Little movement
is identified by "LM." Line or area movement is indicated by a shaft and
barb combination with the shaft indicating the direction and the barbs
the speed. A half barb is 5 knots, a whole barb is 10 knots, and a pennant
is 50 knots.

For example, in Figure 7-1, for the area of snow
and rain over central California, no cell movement is given, but the area
movement is toward the west at 15 knots. Over southern California, no area
movement is given, but the cell movement of the rain showers is toward
the east at 20 knots.

SEVERE WEATHER WATCH AREAS

Severe weather watch areas are outlined by heavy dashed lines, usually
in the form of a large rectangular box. There are two types, tornado watches
and severe thunderstorm watches. Referring to Figure 7-1
and Table 7-2, the type of watch and the watch number
are enclosed in a small rectangle and positioned as closely as possible
to the northeast corner of the watch box. For example, in Figure 7-1,
the boxed "WS036" in South Carolina means the watch area in the southeastern
U.S. is a severe thunderstorm watch and is the 36th severe weather watch
issued so far in the year. The watch number is also printed at the bottom
of the chart (in Mexico) together with the issuance time and valid until
time.

CANADIAN DATA

Radar data from Canadian radar stations are plotted when available.
The stations are Halifax, Holyrood, Mechanics Settlement, Broadview, Elbow,
Vivian, Mont Apica, Britt, Carp, Exeter, Montreal, River Harbour, Upsala,
Villerpy, King City, Carvel, Vulcan, Cold Lake and McGill. The data is
displayed in AZRAN (azimuth-range) format with echo areas outlined by solid
lines. Area, line and cell movements are shown in the same manner as U.S.
data. An alphanumeric code associated with each echo shows, in order, area
coverage, precipitation type, intensity, and intensity trend. Precipitation
type and intensity trend are the same as U.S. data. For area coverage,
a blank designator represents cells, a 1 equals less than 1/10 coverage,
a 4 equals 1/10 to 5/10 coverage, a 7 equals 6/10 to 9/10 coverage, and
10 equals 10/10 coverage. For intensity levels, 0 is very weak, 1 is weak,
2 is moderate, 3 is strong and 4 is very strong. Levels 1 through 4 are
comparable to the U.S. VIP levels of 1 through 4.

Canadian echo top reports are converted from meters to feet and are
plotted to the nearest hundreds of feet MSL For example, 197 is 19,700
feet MSL.

It is sometimes difficult to interpret the data when both U.S. and Canadian
reports are plotted. Do not confuse a Canadian report with a severe weather
watch box. The Canadian radar reports are enclosed by a solid line box,
while a severe weather watch box is outlined by a dashed line.

USING THE CHART

The radar summary chart aids in preflight planning by identifying general
areas and movement of precipitation and/or thunderstorms. Radar detects
ONLY drops or ice particles of precipitation size, it DOES NOT detect clouds
and fog. Therefore, the absence of echoes does not guarantee clear weather,
and cloud tops may be higher than the tops detected by radar. The chart
must be used in conjunction with other charts, reports, and forecasts.

Examine chart notations carefully. Always determine location and movement
of echoes. If echoes are anticipated near the planned route, take special
note of echo intensity and trend. Be sure to examine the chart for missing
radar reports before assuming "no echoes present". For example, the Garden
City (GCK) radar report in southwest Kansas is shown as not available (NA).
There could be echoes in southwest Kansas but be too far away to be detected
by the other surrounding radars.

Suppose the planned flight route goes through an area of widely scattered
thunderstorms in which no increase is anticipated. If these storms are
separated by good VFR weather, they can be visually sighted and circumnavigated.
However, widespread cloudiness may conceal the thunderstorms. To avoid
these embedded thunderstorms, either using airborne radar or detouring
the area would be necessary. Details on avoiding hazards of thunderstorms
are given in Chapter 11, Aviation Weather.

Remember that the radar summary chart is for preflight planning only
and should be updated by hourly radar reports. Once airborne, the pilot
must evade individual storms by inflight observations either by visual
sighting, using airborne radar, or by requesting radar echo information
from FSS Flight Watch. FSS Flight Watch has access to Radar Remote Weather
Displays (RRWDS).

There can be an interpretation problem concerning an area of precipitation
that is reported by more than one radar site. For example, station A may
report RW- with cell movement toward the northeast at 10 knots. For the
same area, station B may be reporting TRW+ with cell movement toward the
northeast at 30 knots. This difference in reports may be due to a different
perspective and distance of the radar site from the area of echoes. The
area may be moving away from station A and approaching station B. The rule
of thumb is to use that plotted data associated with the area which presents
the greatest hazard to aviation. In this case, the station B report would
be the used.